Influence of Atchafalaya River discharge and Winter frontal passage on suspended sediment concentration and flux in Fourleague Bay, Louisiana

Suspended sediment concentrations and fluxes between Fourleague Bay, Louisi ana and the northern Gulf of Mexico were sampled every 3 h for 3 months to examine the importance of atmospheric cold fronts and riverine forcing on t he functioning of this estuarine system. A cold front index was developed a nd used to identify major winter frontal passages likely to have the larges t effects on material concentrations and transport. Suspended sediment conc entrations ranged from 11 to 1527 mg l(-1); the highest values occurred dur ing winter frontal passages and the lowest during calm periods. High concen trations are generated by a continuous source of sediment from the Atchafal aya River and resuspension of benthic sediment via high intensity winds ass ociated with cold fronts along with sufficient duration to keep the sedimen t in suspension. Spring peak discharge of the Atchafalaya River increased w ater levels and sediment concentrations in the bay leading to strong season al net exports of water (1.02 x 10(9) m(3)) and sediment (1.72 x 10(8) kg) into the Gulf of Mexico through Oyster Bayou over the 89-day study. Net flu xes associated with tidal forcing were nearly balanced with a small net exp ort due to freshwater input. The combination of high volumes of water origi nating from the northern bay and the restricted outlet to the Gulf often ca use increased water levels and inundation of the surrounding marshes and po tential advection of sediments onto the marsh surface. The results suggest that marsh drainage often increases the particulate organic carbon export a s a result of marsh flushing. (C) 2000 Academic Press.